Process that Powers the Sun

The Sun is powered by nuclear fusion. In this process protons fuse into helium nuclei. This process is explained step by step on this webpage:

http://zebu.uoregon.edu/~soper/Sun/fusionsteps.html

In short, there are four processes involved:

1) Two protons interact via the Weak Interaction to form a deuterium nucleus, a positron and a neutrino.

2) Positrons annihilate when they interact with electrons, giving rise to photons.

3) Protons collide with deuterium nuclei forming He-3 and a photon. In this process the Strong Interaction is involved.

4) He-3 nuclei when they collide with other He-3 nuclei form He-4 and two protons. The Strong Interaction is also involved here.

The net result is that four protons fuse together to form a helium nucleus, 2 neutrinos, 2 positrons and 6 photons. The energy that is released in this reactions comes from the Strong Interaction. The Strong force binds the quarks in the helium nucleus strongly together. The total energy of the quarks when bound together in the helium nucleus is less than when the quarks are bound in four separate protons. Part of this energy difference escapes in the form of neutrinos which do not interact strongly with matter. But the photons also get a significant fraction of this energy. These photons interact strongly with the matter in the Sun, so the energy of the photons gets transferred to the surrounding matter in the Sun.

The energy difference between the four protons and the helium nucleus which powers the sun is so large that, by Einstein's E = m c^2, Helium (plus two positrons) is lighter than 4 protons.

We can say that the "fuel" is hydrogen and the "waste" is helium and neutrinos. But when the hydrogen runs out, the Sun can burn helium, so one can also argue that the neutrinos are the real waste (the neutrinos also carry away a lot of the fusion energy).

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